Preparation of a-nixro e-caprolactam



y 1963 J. DE HAAN ETAL 3,096,326

PREPARATION om -NITRO a -CAPROLACTAM Filed Feb. 19, 1962 Nitrct ing acid Corbochlor-ide Nitrobenzene C Nitroting E reactor Aqueous 2 phase 8 5 Water 3 O F v .f: X First 3; m J hydrolysis u reactor '3 Nitrobenzene Extract 3 u 3 U J 1 7 qu Phase Separator h Aqueous nitro coprolclctqm solution Aqueous ammonia solutlon Water Organic phase Solution of nitrocgproloctom in nltrobenzene Second hydrolysis reactor I Second extrclctlon column first extraction column Water ih'trobe nzene ,QQMW

3,096,326 PREPARATHQN F a-NITRU e-(IAPROLACTAM Johannes de Haan and Johan l. H. Von Den Hoff, iGeieen, Netherlands, assignors to Stamicarbon N.V., Heerlen, Netherlands Filed Feb. 19, 1962, Set. No. 173,885 Claims priority, application Netherlands Feb. 22, 1961 6 Qiaims. (Cl. 260-2395) The present invention relates to a process for the preparation of oc-IllliIO e-caprolactam. This substance is important as an intermediate product in the synthesis of lysine, one of the essential amino acids, which can be obtained therefrom by hydrogenation and subsequent hydrolysis.

It has already been proposed to prepare a-nitro e-caprolactam by nitration of Z-chloroazacyclo 2,3-heptene 1- carbochloride and hydrolysis of the nitration product in two steps. in the first step the reaction mixture obtained after the nitration is contacted with water at a temperature below 50 C. as a result of which the nitration product is converted to the Water-insoluble 3-nitroazacycloheptane-Z-one l-carbochloride. This substance is separated ofi and, in the second step, further hydrolyzed with fresh water to a-nitro e-caprolactam at a temperature above 50 C. (see Belgian Patents 582,992 and 583,116).

It has now been found that the preparation of OL-l'li-tIU e-caprolactam on a technical scale can be realized in a much simpler manner if the hydrolysis is carried out in a water-immiscible organic solvent for 3-nitroazacycloheptane-Z-one l-carbochloride.

The process according to the invention for the preparation of a-Ili'tlO e-caprolactam by nitration of 2-chloroazacyclo 2,3-heptene l-carbochloride and hydrolysis of the nitration product in two steps, in which in the first step 3-ni-troazacycloheptane-Z-one l-carbochloride is formed, which substance in the second step is hydrolyzed further into a-nitro e-caprolactam, is characterized in that the first step is carried out in a water-immiscible organic solvent for 3-nitroazacycloheptane-2one l-carbochloride, after which the resulting liquid is separated into an aqueous and an organic phase and the latter phase is recontacted with water in the second step.

The nitration can be carried out in accordance with known methods, for instance with 96 to 100% nitric acid, with a mixture of concentrated sulfuric acid and concentrated nitric acid, or with a mixture of nitric acid, sulfuric acid, and sulfur trioxide. In most cases, a small excess of the nitration agent is used.

After the nitration, the reaction mixture is contacted with water and the solvent. By preference a solvent is used which, in the first step of the hydrolysis, does not, or only slightly, react with nitration agent still present.

Suitable solvents are for example chloroform, carbon tetrachloride, chlorobenzene, benzene, benzylalcohol, mixtures of benzene and benzylalcohol, anisole, 2 phenoxyethanol, nitromethane and nitrobenzene. Among these nitrobenzene is to be preferred because it is a relatively good solvent for 3-nitroazacycloheptane-Z-one 1- carbochl-oride and because it is not nitrated to any ap preciable extent under the reaction conditions. Another advantage is that its boiling point is so high that the second step of the hydrolysis can, at the most suitable temperatures, be carried out under atmospheric pressure without there being any danger of evaporation of the solvent. In addition nitrobenzene is also a relatively good solvent for oc-lli'tI'O e-caprolactam.

The amount of solvent need not be larger than the amount needed for dissolving the 3-nitroazacyoloheptane- 2-one l-carbochloride. In most cases, however, a small excess, of say is used.

The acidity in the first step of the hydrolysis is prefer- 3,096,326 Patented July 2., 1963 ably kept at 2-5 N. However, the reaction may also be carried out in a more or less acid medium. A volume of water five or ten times that of the liquid obtained by the nitration usually suflices.

To counteract possible nitration of the solvent, the amount of water used may be increased as the excess of nitrating agent used is larger and/or the solvent is more readily nitrated. It is recommendable to use such an amount of water that the difference in specific gravity between the organic and the aqueous phases forming upon hydrolysis, is large enough to effect rapid separation of the reaction mixture in these phases.

In the first step the temperature is kept below 50 0., preferably below 20 C., to counteract nitration of the solvent and formation of a-nitro e-caprolactam, which is less soluble in the reaction mixture. The reaction is usually completed within 10 to 30 minutes.

Thereafter the reaction mixture is separated into an aqueous and an organic phase, for instance by allowing it to stand for some time, as a result of which the liquid separates into two layers, which are drained off separately.

In the aqueous phase, which contains the bulk of the acid residues, some (x-llitI'O e-caprolactam formed during the hydrolysis, is generally dissolved. This substance can be extracted therefrom with an organic solvent, by preference with the same solvent as was used in the hydrolysis. The extract thus obtained can be re-used as a solvent in the first hydrolysis step. If desired, however, it can first be purified by extracting it with a solution of ammonia in water. From the resulting aqueous solution of its ammonium salt the rx-nitro e-caprolactam can be precipitated by addition of an acid or by heating, as a result of which the ammonia is expelled from the salt.

The organic phase, which mainly consists of the solvent and the 3-nitroazacycloheptane-Z-one l-carbochloride dissolved therein, is re-contacted with water and heated to a temperature above 50 C., by preference below 110 C. A temperature of to C. is preferred. It is recommendable to take care that the solvent cannot evaporate from the reaction vessel during heating. This has the advantage that a purer product is obtained than when the solvent is distilled off during the hydrolysis.

The amount of water used in this second hydrolysis step may widely vary. To prevent undesired side reactions, it is recommended to use at least so much water that upon completion of the hydrolysis the acidity does not exceed 2 N. An acidity of 0.5-1 N is preferred.

If desired, a base, for instance ammonium carbonate, may be added during this step to neutralize the hydrochloric acid set free and thus counteract corrosion of the reaction vessel.

The second hydrolysis step is usually completed Within 10-20 minutes. A portion of the a-nitro e-caprolactam can crystallize already during the hydrolysis, since in the solvents used it tends to dissolve much less readily than 3-nitroazacycloheptane-Z-one l-carbochloride, although the temperature in the second step is much higher than that in the first. Another portion of the a-nitro e-caprolactarn can be crystallized by cooling the reaction mixture. After the crystals have been separated from the liquid, the liquid may be separated into an aqueous and an organic phase from which the wnitro s-CQPI'OlflCtZilTl dissolved therein can be recovered in the way outlined above. After that the solvent can be re-used, if desired after having been freed of dissolved impurities, for example by distillation. The aqueous phase may be used in the first hydrolysis step.

It is advantageous, however, to keep the n-nitro e-caprolactam in solution both during the hydrolysis and dur ing the subsequent phase separation. The continuous execution of the procedure can thus be simplified. The

From this solution a-uitro e-caprolactam with a purity of 99.8% was precipitated by heating.

We claim:

1. In a process for the preparation of oc-IlitIO E-caprolactam by nitration of 2-chloroazacyclo 2,3-heptene 1- carbochloride and hydrolysis of the nitration product in two steps wherein 3-nitroazacycloheptane-2-one l-carbochloride is formed in the first step and said nitro compound is hydrolized further into a-Ilitl'O s-caprolactam, the improvement which comprises carrying out said first step in a water-immiscible organic solvent for 3-nitroazacycloheptane-Z-one l-carbochloride, after which the resulting liquid is separated into an aqueous and an organic phase, and the latter phase is re-contacted with water in the second step.

2. The process of claim 1 wherein the first step of the hydrolysis is carried out at a temperature below 20 C.

3. The process of claim 1 wherein the second step of the hydrolysis is carried out at a temperature of 80 to 4. The process of claim 1 wherein the a-nitro e-caprolactam formed in the second step is kept in organic solution by adding a further amount of solvent in this step.

5. The process of claim 1 wherein the organic phase obtained in the first step is contacted with water in the second step by continuously passing said organic phase successively through a hydrolysis zone and a first extraction zone, while the Water, countercurrently with the organic phase, is continuously passed successively through the first extraction zone and the hydrolysis zone and thereafter through a second extraction zone, the a-nitro e-caprolactam being kept in organic solution by continuouly passing an organic solvent for this material, counter currently with the water, successively through the second extraction zone, the hydrolysis zone and the first extraction zone.

6. The process of claim 1 wherein nitrobenzene is used as a solvent.

No references cited. 

1. IN A PROCESS FOR THE PREPARATION OF A-NITRO E-CAPROLACTAM BY NITRATION OF 2-CHLOROAZACYCLO 2,3-HEPTENE 1CARBOCHLORIDE AND HYDROLYSIS OF THE NIRATION PRODUCT IN TWO STEPS WHEREIN 3-NITROAZACYCLOHEPTANE-2-ONE 1-CARBOCHLORIDE IS FORMED IN THE FIRST STEP AND SAID NITRO COMPOUND IS HYDROLIZED FURTHER INTO A-NITRO E-CAPROLACTAM, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT SAID FIRST STEP IN A WATER-IMMISCIBLE ORGANIC SOLVENT FOR 3-NITROAZACYCLOHEPTANE-2-ONE 1-CARBOCHLORIDE, AFTER WHICH THE RESULTING LIQUID IS SEPARATED INTO AN AQUEOUS AND AN ORGANIC PHASE, AND THE LATTER PHASE IS RE-CONTACTED WITH WATER IN THE SECOND STEP. 